Postage representing payment for a postal service makes up a significant portion of expenses of many businesses. For example, an insurance company routinely sends a large number of bills and correspondence to customers via mail, thereby incurring substantial postage.
To facilitate mailing of a large volume of mail, a franking system is often employed to frank, on mailpieces, postage indicia which serve as proof of postage. One such franking system may be a postage meter, or general purpose computer equipment, e.g., a personal computer (PC), having appropriate software installed therein for printing postage indicia using a local/network printer.
To secure accounting of postage dispensation, some postal authorities, e.g., the United States Postal Service (USPS), advocate use of a postal security device (PSD) in a franking system. For example, the USPS promulgated specifications for the design of the PSD under an Information-Based Indicia Program (IBIP).
In general, a PSD has a secure housing, and within the secure housing are accounting registers and a cryptographic engine. These accounting registers typically include an ascending register and a descending register. As is well known, the ascending register is used to keep track of the amount of postage dispensed. On the other hand, the descending register is used to keep track of the amount of postage available for postage dispensation. The cryptographic engine is used to sign certain postal information contained in a postage indicium to authenticate the same, in accordance with a well known public key algorithm. One such public key algorithm may be the Digital Signature Algorithm (DSA) described, e.g., in “Digital Signature Standard (DSS),” FIPS PUB 186, May 19, 1994. The cryptographic engine also carries out cryptographic authentication and signing for communications of the PSD with a remote data center, which may be maintained by a party other than a postal authority, e.g., a postage metering equipment or service provider. Such communications may be used to set up and maintain the PSD, and to replenish the postage fund by adjusting the value of the descending register in the PSD, in accordance with a well known telemeter setting (TMS) technique.